The present invention concerns a device for a submersible machine, such as a pump, a turbine or a mixer.
A machine of this type normally includes an electrically driven motor and a hydraulic unit with an impeller connected to the motor via a rotary driving shaft. In order to prevent the medium within the hydraulic unit from flowing along the shaft and penetrate the electric motor and cause damage, one or several seals are arranged between the motor and the hydraulic unit. A common type of seal is the so-called mechanical face seal, which comprises one seal ring rotating with the shaft and one stationary seal ring mounted in the surrounding housing. The two rings are pressed together by spring force thus preventing medium from penetrating between them.
If the medium within the hydraulic unit contains pollutants, a special problem occurs. As the pressure within the hydraulic unit is higher, pollutants may penetrate between the seal surfaces cause damage, meaning that the seal resultantly deteriorates or fails totally.
In order to solve this problem it is common to arrange two mechanical seals with an intermediate room filled with a barrier liquid such as oil, which lubricates and cools the surfaces. By this the seal adjacent the electric motor will always operate with a clean medium and thus the risks for damages will decrease drastically. If the seal adjacent the hydraulic unit should be damaged, medium from said unit may enter the barrier liquid room, but by controlling said liquid at regular intervals, the seal could be repaired or replaced before any serious damage has accured. An example on such a design is shown in the Swedish patent No 381 318.
If it has been noted that the barrier liquid has been too diluted by the medium in the hydraulic unit, the seal adjacent said unit must be replaced. If the dilution has been considerable, there is a risk that also the other seal has been damaged and therefore it might be preferable to replace both seals at the same time.
In order to make such a replacement easier, it has been suggested to arrange them in one single unit which makes service easier and increases the reliability. Examples on such designs are shown in the Swedish patents 200 144 and 466 925.
In order to obtain a good circulation of the barrier liquid within the seal unit, it has been suggested to arrange a pump within the latter. Especially in a case where it has been chosen to use a closed cooling system for the electric motor using the barrier liguid as a coolant, a pump is necessary if a sufficient flow should be obtained.
Known designs such as those shown in the Swedish patent 327 904 have however certain disadvantages concerning space demand and efficiency. This invention concerns a device which in an effective and secure: way obtains the necessary circulation even at a low rotation speed and which has a very limited space demand.
A seal device in the form of an easily exchangeable unit for a rotary driving shaft between an electric motor and a hydraulic unit, the seal device comprises first and second mechanical face seals having an intermediate room for a barrier liquid. The first mechanical face seal includes a first stationary seal ring and a first rotary seal ring and the second mechanical face seal includes a second stationary seal ring and a second rotary seal ring. A pump is provided for circulating the barrier liquid in the intermediate room. A cylindric spring housing that rotates with the shaft is connected to the first rotary seal ring with a first driver. The spring housing includes a second driver for driving the second rotary seal ring. The spring housing operates as a seat for a biasing element that urges the second rotary seal ring towards the second stationary seal ring and further operates as a hub for vanes in the pump. The outer pump housing wall of the pump is formed by first and second holders which are respectively for the first and second stationary seal rings.